A test of time dilation with an optical atomic clock on a stratospheric balloon

平流层气球上光学原子钟的时间膨胀测试

• 批准号: 323210209
• 负责人: Professor Stephan Schiller, Ph.D.
• 金额: --
• 依托单位: Institut für Experimentalphysik
• 依托单位国家: 德国
• 项目类别: Research Grants
• 财政年份: 2017
• 资助国家: 德国
• 起止时间: 2016-12-31 至 2022-12-31
• 项目状态: 已结题
• 来源: https://gepris.dfg.de/gepris/projekt/323210209?language=en
• 关键词: test; time; dilation; optical; atomic

The performance of state-of-the-art optical lattice clocks offers an opportunity for an improved test of one of the fundamental effects of General Relativity, the time dilation in the gravitational potential. The most precise test of this effect was performed 40 years ago by comparing two microwave clocks on a 10 000 km height difference. A new, non-satellite test of this effect with a competitive precision necessarily implies the need to operate an optical clock outside of the laboratory. Here we propose to build a ytterbium optical lattice clock and to use it as a probe clock on significant altitudes to precisely measure the gravitational time dilation through a frequency comparison with a reference clock on the ground. We aim at a precision of the measurement better than that of the upcoming space mission ACES (2017-18), which employs a cold-atom Cs microwave clock. To achieve the goals of the project, we propose to develop a flyable optical clock (FOC), a particularly compact and robust apparatus, which additionally comprises, for the first time, two atomics subsystems, allowing for in-depth characterization and optimization of performance towards our specific experiment. In order to relax the requirement of accuracy for both the probe and the reference clock, in our application we foresee that during each experiment they are first compared on ground, before the FOC is brought to altitude and the comparison is repeated. Thus, the main requirement is the reproducibility of the FOCs and the references frequency. Furthermore, achieving high frequency stability is crucial in order to minimize the integration time during the measurement campaign, whose duration is limited. In a 7-year long project, we plan to perform experiments of increasing complexity, concerning both the vertical distance and the link between the two clocks. In a demonstration experiment (year 4), the FOC will be operated in the panoramic level of the television tower in Düsseldorf, 160 m above the reference clock on ground, which is connected through a fiber link and intercompared. This will provide a test of the gravitational time dilation at the 1E-3 level. In the final part of the project (years 7), a mission will be performed in which the FOC will be operated on a stratospheric balloon at an altitude of 35 km for approximately 10 hours. The frequency link for comparison with the reference clock on ground will be a frequency-comb-based two-way free-space laser link, to be implemented in collaboration with colleagues from NIST and ViaLight in years 4-6. By averaging down the statistical uncertainty of the frequency difference of the FOC and reference clock to the 2E-18 level, we aim for a measurement of the gravitational time dilation with relative uncertainty of 5E-7, approximately a factor of 4 better than the expected goal of the ACES mission.

最先进的光学晶格钟的性能为改进广义相对论的基本效应之一（引力势的时间膨胀）的测试提供了机会。 40 年前，通过比较高度差为 10,000 公里的两个微波钟，对这种效应进行了最精确的测试。以具有竞争力的精度对这种效应进行新的非卫星测试必然意味着需要在实验室外操作光学时钟。在这里，我们建议建造一个镱光学晶格钟，并将其用作重要高度上的探测钟，通过与地面参考钟的频率比较来精确测量重力时间膨胀。我们的目标是测量精度优于即将推出的太空任务 ACES (2017-18)，该任务采用冷原子 Cs 微波时钟。为了实现该项目的目标，我们建议开发一种可飞行光学时钟（FOC），这是一种特别紧凑且坚固的设备，它还首次包含两个原子子系统，可以针对我们的具体实验进行深入的表征和性能优化。为了放宽对探头和参考时钟的精度要求，在我们的应用中，我们预计在每次实验期间，首先在地面上对它们进行比较，然后将 FOC 带到高空并重复进行比较。因此，主要要求是 FOC 和参考频率的再现性。此外，为了最大限度地减少持续时间有限的测量活动期间的积分时间，实现高频率稳定性至关重要。在一个为期 7 年的项目中，我们计划进行越来越复杂的实验，涉及垂直距离和两个时钟之间的链接。在演示实验（第 4 年）中，FOC 将在杜塞尔多夫电视塔的全景层运行，位于地面参考时钟上方 160 m，通过光纤链路连接并相互比较。这将提供 1E-3 级引力时间膨胀的测试。在该项目的最后部分（第 7 年），将执行一项任务，其中 FOC 将在高度 35 公里的平流层气球上运行约 10 小时。用于与地面参考时钟进行比较的频率链路将是基于频率梳的双向自由空间激光链路，将在第 4-6 年与 NIST 和 ViaLight 的同事合作实施。通过将 FOC 和参考时钟的频率差的统计不确定性平均降低到 2E-18 水平，我们的目标是测量相对不确定性为 5E-7 的引力时间膨胀，大约比 ACES 任务预期目标好 4 倍。